The renaissance of functional ¹⁸F-FDG PET brain activation imaging

Excerpt

For a few years now, positron emission tomography (PET) has benefited from a renaissance of functional imaging through ¹⁸F-FDG PET brain activation studies. The first PET studies involving activation brain imaging nevertheless emerged in the 1980s, using intravenously administered oxygen-15-labelled water (¹⁵O-water) [1, 2]. This approach was used to measure regional cerebral blood flow (rCBF), and has been shown to be a sensitive method for quantifying regional brain activation during specific tasks [3, 4]. Such functional imaging studies proved extremely useful for mapping brain activation patterns involved in cognitive tasks such as word reading, mental imagery, timing or memory [5, 6]. The first clinical validations of quantitative analyses using Statistical Parametric Mapping (SPM, Wellcome Trust Centre for Neuroimaging, London, United Kingdom) were thus performed with PET imaging [7]. These PET imaging studies preceded the emergence of functional magnetic resonance imaging (fMRI) in the 1990s, which depicts the engagement of different brain regions within a distributed system through fluctuations of the blood-oxygen-level dependent (BOLD) signal [8]. fMRI applications have since been extended to reveal additional information about the degree to which components of large-scale neural systems are functionally coupled together to achieve specific tasks. This phenomenon underpins the study of functional connectivity, which is mathematically defined as the statistical association between two distinct time-series, i.e. the connectivity between brain regions that share functional properties. The fMRI approach enables the study of functional connectivity within single subjects or groups through serial imaging of the brain in the so-called resting state (i.e. without any specific stimulus or task) or in a condition of task-dependent activation [9]. …